Calculating device



6 Sheets-Sheet 1 Filed July 29, 1940 INVENTOR.

A; 5527' ThQwe/s.

1943. A. T. HARRIS 2;307,584

CALCULATING DEVICE Filed July 29, 1940 6 Sheets-Sheet 2 EZ'G.Z. T] I L7 w lmfils/er THAI/PEAS. INVENTOR.

Jan. 5, 1943. A. T. HARRIS CALCULATING DEVICE Filed July 29, 1940 s Sheets- Sheet s INVENTOR.

Jan. 5, 1943. A. T. HARRIS CALCULATING DEVICE Filed July 29, 1940 5 Sheets-Sheet INVENTOK ALBERT 7. fume/s.

-f00 gw ll ml] Jan. 5, 1943. A. T. HARRIS 2,307,584

CALCULATING DEVICE Filed July 29, 1940 e Sheets-Sheet s 5 w W WW mm. h J o w A m 2 h l H a 7 r w e 4 M n A a). I D %/Z A 9 w a y m 5 5M 9 .W 4 w A 0. l I Y I 1 W W F W s YIHII a W W.

2 IIIIIHHZV 'cision reading of the angles.

Patented Jan. 5, 1943 FFICEE CALCULATING DEVICE Albert T. Harris, New ,York, N. Y., assignor to Cal-Ku-Scope Inc., New York, N. Y., a corporation of New York Application July 29, 1940, Serial No. 348,132

20 Claims.

This invention pertains to calculating devices and more particularly to a device for use in conjunction with mechanically calculating problems having trigonometric and/or geometric functions, and is a geometrical instrument for Working out problems by setting the device with known angles and measurements and obtaining the result by observation.

Heretofore, no mechanical device has been provided for doing trigonometric and geometric problems mechanically, and this invention contemplates mechanically calculating such problems where three or more angles are involved.

The present invention embraces certain fundamental functions which are clearly set forth in my copending application Serial Number 344,571 and also utilizes new basic functions and modifications thereof which are disclosed in this application.

In the present invention, four dimensions may be utilized in that four sides of a geometrical figure may be used in conjunction with the afore associated angles. All four sides of the calculating device are connected by pivotal means, and the members representing the four sides eachare raduated and have Vernier rules associated therewith for precision reading. The four angles each have protractors which may be read in conjunction with the protractor vernier for preare used on each of the sides of the four fundamental angles for manipulating with precision the movement of the pivot point of one angle in relation to an adjacent side. so that three angle problems may be Worked out, which is done by sliding two opposite sides together so that they have a common pivot point for mechanically calculating problems.

An intermediate arm is introduced in the instrument for working out problems involving angles within the confines of the four fundamental angles and also for determining the length of the side represented by the intermediate arm.

The instrument also may be used for obtaining sights on distant objects to obtain the distance from said object or to mechanically read the dimensions thereof such as height and width, and thereafter utilizing a simple mathematical formula to conclude the problem.

While the calculating device set forth has many Threaded means Provisions are made straightedges with sliding members associated therewith to obtain three, four, and more angles, and/or lengths of the associated sides involved in the problems.

A further object of the invention is to provide a geometrical instrument which uses sights as a part of said instrument to take certain measurements and/or angles regarding distant objects such as elevation and width of the object and distance therefrom.

Further objects of the invention may be and may become apparent to those skilled in the art from. a perusal of the following specifications and drawings.

In the drawings:

' Fig. 1 is a plan view of the basic calculating device.

.Fig. 2 is an enlarged plan view of broken away.

.Fig. 3 isa front View of, Fig. 1.

Fig. 4 is a cross-section taken along lines 44 of Fig. 2 to show the internal construction of the secondary member and associated parts.

Fig. 5 is a cross-section taken along lines 5-5 Fig. 1 partly of Fig. 2.

Fig. 6 is a side'view of Fig. 2 partly broken away. V

Fig. 7 is a cross-section taken along lines 7-1 of Fig. 2.

Fig. 8 is a modification of Fig. 1 with additional parts for solving mOre intricate problems, primarily for taking sights.

Fig. 9 is a view showing the left master and right master arms at 90 degrees angle, associated with the intermediate arm and disc rule.

Fig. 10 is a sectional view taken along lines I0 l0, of Fig. 9 shown in relation to the master base.

Fig. l1 is a View taken along lines Il-Il of Fig. 9 to show the cross rule folded back into the intermediate arm.

Fig. 12 is a modification of means for manipulating the threaded operating member of certain of the master arm controls. 7

Referring to the drawings and more particularly to Fig. 1, the master base It has a primary member M comprising a primary base 15 and'primary slide it. The primary base It is fixed in relation to longitudinal movement With the master base. The left master arm IT is pivoted at I8 to the slide 1 6. The right master arm i8 is pivoted to the primary base 85 at substantially a point is. The screw 2!! is held in position by stops 2|, while the screw 22 is held in position in relation to the base by stops 23. Screw 2 is threadedly connected to the slide it andrthe screw 22 threadedly connected to the base I5, so that there may be relative movement between each base and slide by manipulation of the screws and 22.

The secondary member 24 has a secondary base 25 and secondary slide 25, which slide moves along grooves in the secondary base 25. The left master vernier 27 moves along the left master arm ll, said left master Vernier being pivoted substantially at a point 28. The right master arm carries the right master Vernier 35 which is secured to the secondary base 25 and pivoted at a point 29. The secondary member 24, therefore, has longitudinal movement supported by the left and right master vemier and one Vernier may be moved in a greater distance along its respective master arm than the other Vernier, so that any, angular relation may be had between the primary member, secondary member, left master arm and right master arm. Screws 3i and 32 are the left and right secondary screws respectively for lateral movement of the left and right master arms respectively. Screw 3| is pivoted at point 33, while screw 32 is pivoted at point 34. Angle irons 35 and 36 are secured to the master base, carrying swivel boxes 37 and 3B which have threaded members 39 and 40 (Fig. 2) which permit the screws to be rotated by turning the knurled members 4i and 42 respectively. The free ends of the screws 3i and 32 are pivoted in the extensions 43 and 44 respectively, which extensions are fastened to the free ends of the left and right master verniers respectively, by any convenient means such as screws 45. The extensions 43 and 44 have shoulders such as 43 on either side of a working member 41 which is pivoted to the extension such as 43. By this arrangement, it will be seen that a rotation of the knob 42 will cause the free end of its respective master arm to move depending on direction of the rotation of the knurled member such as 42.

While the four screws 29, 22, 3| and 32 are shown at the outer ends as having means which require them to be screwed in and out through the entire length of the screw it is to be understood that any convenient means may be used to provide more rapid manipulation by having means which can be moved along the screws and then looked to afford manipulation of the screw thereafter substantially similar to the arrangement hereinafter explained in regards to the manipulation of the left and right master W verniers.

Referring particularly to Fig. 2, there are shown parts for general manipulation of the left and righth master verniers. Referring particularly to Figs. 2 and 5, clamp 48 is shown having tongues 49 and 50 which slide in grooves and 52. The clamp 48 is connected to the master Vernier by screw 53 and is threadedly engaged in such clamp so that a rotation of the screw 53 by the knurled member 54 in the proper direction will cause the clamp to be securely locked at its respective master arm such as I1. One end of a screw 55 is secured to the master Vernier such as 21, while the free end thereof threadedly engages the knurled nut 55 so that rotation of the nut 56 when the screw 53 is locked against the master arm, will cause the vernier to move to and fro along its respective master arm. This operation is the same for the right master Vernier.

The left secondary protractor 52 is secured to the secondary base by any convenient means such as screws. The left secondary Vernier 62' is secured to the left master vernier by means of screws, while the right secondary Vernier 6| is secured to the right master Vernier by any convenient means such as screws. By this arrangement it Will be seen that any longitudinal movement of either master vemier will vary angles C and D and that this angular relation may be read on the secondary left and right protractors in conjunction with the secondary left and right vemiers.

The primary member 24 has a left primary protractor G2 and a left primary Vernier 63, the left primary protractor being secured to the left master arm while the left primary Vernier is secured to the slide I 8 by means of screws 54. The right master protractor 65 is secured to the right master arm while the right primary Vernier 66 is secured to the primary base l5 by the means of screws 57. It will, therefore, be seen that as the left arms are moved on their respective pivot points I8 and l9, the angles A and B will be varied and their angles read on the protractors 52 and a left primary Vernier 63, the left primary protractor being secured to the left master arm while the left primary Vernier is secured to the slide it by means of screws 64. The right master protractor 65 is secured to the right master arm while the right primary vernier 65 is secured to the primary base I 5 by the means of screws 61. It will, therefore, be seen that as the left arms are moved on their respective pivot points 18 and 19, the angles A and B will be varied and their angles read on the protractors 62 and 65 respectively in relation to their verniers 63 and 66.

A small scale E8 is secured to the master base portion which small scale has readings thereon, so that when the zero reading 69 engages a graduation indicating a zero reading 2% on the base member [5, it is indicated that the pivot point I9 is exactly in the lateral center of the master base. Verniers H and 12 are used in conjunction with the scales l3 and '54 respectively. The verniers l5 and T5 are read in conjunction with scale H and 78 respectively, so that the exact reading may be obtained between the discs of l the various pivot points. It will be seen that the zero readings of the verniers l5 and it and also 12 and 13 of the primary member is directly below the graduated edge of the left master arm when the left master arm has the angle A at'90 degrees with the primary member 24. It will be noted that the zero readings on the secondary base member are on the graduated edge of the right master arm in line with the zero readings on the primary member when the angle B is 90 degrees from the primary member.

A more detailed construction of the apparatus 7 will be shown in the cross sectional view of Fig. 4

shown in conjunction with the front view of Fig. 3. The left master Vernier has the left secondary Vernier 69 secured thereto by screws such as 19 and the peripheral edge of said Vernier as adjacent to the left secondary protractor. The slide 26 is pivotally connected to the left master Vernier 21. A plate 28 has. one end thereof secured to the lower portion of the left master verm'er by means of screws 23. The plate 28 has a hub 80 which fits into a metallic shield 8! which shield is secured into the slide proper. The hub of the plate 28 which is attached to the left master Vernier is held in pivotal relation with the shield 8| which is securely fixed in the slide by means of a screw 82, which screw is threadedly connected into the hub. It will therefore, be seen that the slide can be turned in relation to'the master Vernier.

The right master Vernier 33 has a hub 83 as a part thereof. A strap 84 goes completely around the base member and is secured thereto by means of a screw 85. The upper portion of the strap has a hub 85 thereon which fits into the shield 81, which shield is driven into the hub 83 to provide a working surface between the shield as part of the right master vernier and the hub 86 as part of the secondary base. While the strap 84 is shown adjacent the master base i3 is to be understood that there is no friction there between since the strap may ride on the master base l3 to carry part of the weight of the instrument if it is so desired. It will, therefore, be seen that the movement of the right master vernier may be had through the rotatable axis provided within the construction of the hub 83.

The front view in Fig. 3 shows the working members such as 48 with shoulders 46 on either side thereof, of each of the working members so that the rotation of the knobs 4i and 42 will give lateral movement to the free ends of the master arms. Since the working members 4? are pivoted about pins 38 which protrude from opposing sides of the working member.

Fig. '7 shows detailed construction of the con-.

nection between the secondary slide 26 and the left master vernier 2'8. The screws 29 are seen holding the plate 28 in fixed relation to the left master vernier, which plate is pivotally connected to the slide by means of the screw 82.

The primary slide M has a guide member 81 on the lower portion thereof, which guide member is secured to the master base by any convenient means such as screws. The rear guide member 88 is connected to angle irons 35, leaving a space between the guide member 88 and the base [3. In this manner the primary base may slide on the guides 81 and 88 so that the base will be always held in a fixed position in relation to the master base to assure accuracy in the readings of the various protractors and rules. The hub 89 is attached to the far end of the left master vernier by a screw 93 in'substantially the same manner as is screw 32 which connects the secondary slide to the left master vernier. The adjacent screws 28 and 22 are shown threadedly connected to their respective members. A shield SI is afiixed to the slide l8 and the lower portion of the hub 89 extends thereinto, so that the screw 91! will permit a pivotal joint between the left master arm and the primary member by means of the primary slide l8. 1* will be noted that the upper portion of the hub 89 has a circular detent 93 therein, the purpose of which will be set out in detail later in this specification.

The view shown in Fig. 6 is substantially selfexplanatory but is partly broken away to show the protractor 59, which is mounted onto the semi-circular head 9 3 which is an integral part of the secondary base member 25 of the secondary member 24 as a unit. The right secondary vernier 6! is shown with its peripheral edge adjacent the right secondary protraotor 59.

The view shown in Figs. 9 and embrace the modification which permits a disc 'protractor 95 to be secured to the rule and more particularly to the hub 89 on the far end of the left master arm. A spring snap 9B is secured by a headed pin 91 to the center of the disc protractor, which disc pro-tractor has the snap 96 urged into the opening of the upper part of the hub. The ridge of the snap fit into the detent 93 more clearly shown in Fig. '7. A disc base 98 has grooves therein to receive the tongues of the slide 98 which slide is pivotally connected to the intermediate arm lllfi. The disc protractor is graduated and is read against the disc vernier llll. Referring to Figs. 8 and 9 particularly, it will be seen that the intermediate arm I fit has an intermediate arm slide ifl2, which is preferably of transparent material and'is mounted on the arm as by a pin ass, and is pivotally mounted to an intermediate base slide, the lower side of which base slide has tongues iii iwhich slide in grooves Hi5. base slide can be read against either scale of the base and coincide with the zero reading on the slide Hit. A cross rule tilt; is pivoted on the same point as the intermediate arm its to the disc rule H3? at pivot point N18. The graduations on the disc rule it? are read against the disc rule vernier I69. The disc rule has a member preferably transparent i it, which slides thereon and has a pin iii which is suspended downwardly and nearly touches, or may touch the graduated portion of the left master arm.

While the drawings indicate that the slides It? and H6 are transparent, it is to be understood that they may be made out of any suitable opaque or translucent material, and may be wholly or partly transparent as the desires of the case may dictate. The master arm is set forth as being transparent but it is to be understood that this maybe made of any opaque material such as steel, or other equivalents may be introduced to correspond with the necessary changes without departing from the spirit of the claims.

The calculating device as set forth, -not only may be used for figuring geometrical problems that can be set up on the scale with certain known angles and measurements, but the device may also be used where it is desirable to sight objects beyond the confines of the master base. With this in mind, sights are located at convenient places on the apparatus for the purpose of determining mechanically the distance from a known object, or the size of the object such as the height and width.

To this end, a sight 5 i2 is located on the right master vernier. On the far end of the right master arm is an extension H3 having a sight H4 affixed thereto. A sight I I5 is located on the left master vernier while a sight He is located on the far end of the left master arm.

Referring to Fig. 9, the left and right master arms have been moved together so that the center of the hub 89 has moved over the center pivot point lie of the right master arm. The bracket H3 carrying the sight Hal has been described as being fixedly connected to the far end of the right master arm, and a portion about the pivot point is shown dotted, indicating that this portion is below the surface of the primary member. The member H3 is a U shaped member having the top leg secured to the far end of the right master arm by any convenient such as screw 922, while the lower leg of the U shaped bracket MS has a fiange H5 thereon, which flange extends about the boss 528 and is securely connected thereto at the lower portion of the boss. The U shaped member H3 is so shaped because it is necessary, when in position shown in Fig. 9, to swing about at an angle, and in order-to do this it must move about the guide 38. A screw l2! goes through the boss 52%, and into a tubular member 5253 which is secured into a hole E38 in the primary base. The screw H2 is shownv securing the upper end of the bracket 2 53 to the tip of the far end of the right master arm with the sight Iiifixed thereto. The bracket 523 is secured to the far end of the left master arm by screws such as shown for securing the sight bracket l 13 to the right master arm. The sight The vernier readings on the intermediate I I5 has a dotted portion I25 which indicates that the sight H5 may be thrown back to an ofi-normal position when it is necessary to bring the left and right master arms in close proximity to one another.

The intermediate arm 59%] has a sight I25 near the pivot point thereof, while the sight IE6 is on the free end thereof, which sights have their hairline centers in line with the pivot points of the intermediate arm and the pin E63 on transparent slide "32.

Fig. 11 shows the intermediate arm I00 with the pin I 27 connecting same to-the disc rule I91. The cross arm IDS is pivoted on pin I21 by the shoulder I28. The pin I21 has heads on either end thereof to hold the parts intermediate its length in relation one to the other.

The modifications shown in Fig. 12 is used when the master arms are required to be moved nearer the sides of the device than would be permitted for efficient operation if the bracket 31 for screw 3|, was permanently fixed to the flange 35. In Fig. 12 the master base I3 has the flange 35 secured thereto which flange has a groove I3I below a slot I32 which groove and slot are substantially the length of the flange. The bracket I33 is similar to bracket 31 with a clamp I34 secured thereto having a tongue I35 thereon which rides in the groove ISI A clamp screw I 36 is threadedly connected to the clamp and is used to lock the clamp in a fixed position along the master base flange 35.

When the master arms are at right angles as shown in Fig. 9, the disc slide may be rotated so that the zero reading of the disc protractor is in registry with the zero reading of the disc Vernier, indicating that the pivot point H38 of the intermediate arm is directly over the front edge of the graduated right master arm.

Knowing the distance on the disc slide, it is possible to set the intermediate arm parallel with the left master arm. The intermediate arm may be moved into alignment with the disc rule by having the ball point, I31, engage the detent I35;

so that angular readings may be taken about the pivot point I8 of the left master arm. The cross rule I06 will register the distance from the pivot point I08 of the intermediate arm to the graduated front edge of the left master arm. It will be seen that many angles and problems may be worked with this arrangement and that distances and angles used on problems involving such angles and measurements within the confines of the four angles A, B, C, and D.

In order to obtain a distance from a given point a beyond the confines of the master base the operator of the device may sight the distance point through the sights I I2 and I M so that the center hairlines thereof are properly aligned, and this operation may be repeated by keeping the right master arm stationary and manipulating the left master arm so that the hairlines of the sight I 25 and H6 of the left master arm are properly aligned with the distant point. By observing the device, it is possible to apply a simple mathematical formula to mathematically calculate the distance from the instrument to the distant point. The sights I25 and I26 on the intermediate arm may also be used in much the same manner as the sights on the master arms for any desired purpose. From the foregoing, it will be seen that the objects set out herein may be readily accomplished.

The device is not restricted to the specific parts and construction embraced in the disclosure, but

may be modified or changed in any manner to embrace any and/or all equivalents within the scope of the annexed claims.

What is claimed as new and desired to secure by Letters Patent of the United States is:

1. A geometrical instrument of the class described comprising a slidable primary member, a slidable secondary member, said primary and secondary member each comprising a base portion and a slide portion, and a pair of graduated master arms, each of said master arms being res-pectively pivotally connected to the primary and secondary members, and protractor means for registering the angle at each of the pivotal connections of the members.

2. A geometrical instrument as set forth in claim 1 wherein one of said master arms is connected on one end to one portion of the primary member and the other end thereof connected to one portion of the secondary member, the other of said master arms being connected to the remaining portion of the primary member while the opposing end of said remaining arm is connected to the remaining portion of the secondary 3 member.

3. A geometrical instrument as set forth in claim 1 having a master base for mounting the primary and secondary members, side supports mounted on the master base, and threaded means rotatably mounted on the side supports and threadedly connected to the slidable primary member to provide lateral movement therefor.

4. A calculating device of the class described comprising a pair of spaced master arms, a slidable primary member, a slidable secondary member, the primary and secondary members each comprising a base portion and a slide portion, means for pivotally connecting one end of each of said master arms to the slide and base portions of the primary member, and means for connecting each of the opposing ends of the master arms to the slide portion of the secondary member.

5. A calculating device as set forth in claim 4 wherein means is provided whereby the master arms afiixed to the primary member may be brought together to have a common pivot point.

6. A calculating device of the class described as set forth in claim 4 wherein each of the master arms has a slide on either end thereof for determining the angular relation of a point of a given object beyond the confines of the master base.

'7. A calculating device of the class described as set forth in claim 4 wherein each of the master arms has a slide on either end thereof for determining the angular relation of a point of a given object beyond the confines of the master base and a protraotor is afiixed about each of the pivot points to determine the angle of the adjacent sides of the calculating device.

8. A calculating device of the class described as set forth in claim 4 wherein each of the mas ter arms has a slide on either end thereof for determining the angular relation of a point of a given object beyond the confines of the master base, including a protractor afiixed about each of the pivot points to determine the angle of the adjacent sides of the calculating device, and a iprotractor vernier adjacent each of said protractors for a more precise reading of the angle of the adjacent sides.

9. A calculating device of the class described comprising a pair of spaced graduated master arms, a slidable primary member, a slidable secondary member, the primary and secondary members each comprising a base portion and a slide portion, means for pivotally connecting one end of one master arm to one portion of said primary member and means for connecting the other end of said master arm to one portion of the secondary member, means for pivotally connecting one end of the remaining master arm to the remaining portion of the primary member, means for pivotally connecting the opposite end of the remaining master arm to the remaining portion of the secondary member, protractor means on each of said portions of the primary and secondary members to register the angular relation between each of the master arms and its adjacent primary or secondary member.

10. A calculating device of the class described comprising a pair of spaced, graduated, master arms, a slidable primary member, a slidable secondary member, the primary and secondary members each comprising a base portion and a slide portion, means for pivotally connecting one end of one master arm to one portion of said primary member and means for connecting the other end of said master arm to one portion of the secondary member, means for pivotally connecting one end of the remaining master arm to the remaining portion of the primary member, means for pivotally connecting the opposite end of the remaining master arm to the remaining portion of the secondary member, protractor means on each of said portions of the primary and secondary members to register the angular relation between each of the master arms and its adjacent primary or secondary member, a disc protractor pivotally mounted at one of the pivot points, connecting one of said master arms to its respective portion of the primary member, a disc rule slidably connected to the disc protractor, and intermediate arm connected to one end of the disc rule, and slide means operable along said intermediate arm movably connected to an intermediate base slide engaging one portion of the secondary member.

11. A calculating device of the class described as set forth in claim wherein the pivot point connecting the intermediate arm and the disc rule is common to a pivot point for a cross rule, slide means on said cross rule, and means on said slide dependent therefrom to register with graduations on the master arm.

12. A geometrical instrument having a master base, a pair of supports connected to the base, a primary member mounted on said supports, a pair of master arms mounted on said primary member, a secondary member also mounted on said supports, said secondary member comprising a base portion and a slide portion, said base portion being pivotally connected to one end of one master arm and the slide portion being pivotally connected to one end of the other master arm, and a protractor means about each of the pivotal points to register the angle among the several aforementioned arms.

13. A geometrical instrument as set forth in claim 12 having pivotal means for connecting the one end of each of the master arms to the primary member.

14. A geometrical instrument having a master base, a pair of supports connected to the base, a primary member mounted on said supports, a pair of master arms pivotally mounted on said primary member, a secondary member also mounted on said supports, said secondary member comprising a base portion and a slide portion, said base portion being pivotally connected to one end of one master arm and the slide portion being pivotally connected to one end of the other master arm, a protractor means about each of the pivotal points to register the angle among the several aforementioned arms, and a pair of adjustment means mounted on said supports, one end of one of the adjustmentmeans being threadedly connected to one portion of the secondary member and one end of the other of the adjustment means being threadedly connected to the remaining portion of the secondary member.

15. A calculating device of the class described comprising a base, a plurality of interslidable means slidably associated with said base, master arms connected with the interslidable means, pivotal means forming the connections whereby said arms may assume angular positions with respect to the direction of sliding movement of said interslidable means and each other, and means associated with one of said pivotal connections whereby one of the arms may be selectively attached thereby providing for association of two arms at the same connection to provide for a common vertex for said arms.

16. A calculating device of the class described comprising a base, a plurality of interslidable means slidably associated with said base, master arms connected with the interslidable means, pivotal means forming the connections whereby said arms may assume angular positions with respect to the direction of sliding movement of said interslidable means and each other, and a detachable connection at one of said pivotal connections whereby one of said arms may be brought into detachable pivotal association with another of said arms to provide a common vertex.

17. A calculating device of the class described comprising a base, pairs of slide members shiftably carried on said base in spaced opposed relation and movable relative to each other, a master arm connected with one slide member of each pair of slide members and bridging the base and power means associated with said base for positively effecting movement of said slide members.

18. A calculating device of the class described comprising a base, pairs of slide members shiftably carried by said base in spaced opposed relation and movable relative to each other, a master arm connected with one slide member of each pair of slide members, means pivotally connecting each end of the arm with its respective slide member, and power means for positively moving said slide members.

19. A calculating device of the class described comprising a base, pairs of slide members movably carried on said base in spaced opposed relation and movable relative to each other, a pair of master arms each connected with opposed slide members of each pair of slide members, means movably connecting each arm to its respective slide members and positive power means for efiecting minute adjustments of said slide members.

20. A calculating device of the class described comprising a base, pairs of slide members movably carried on said base in spaced opposed relation and movable relative to each other, a pair of master arms each connected with opposed slide members of each pair of slide members, means pivotally connecting each arm to its respective slide members, protractor means at each pivotal connection for determining the angular relation of each arm at its pivot and positive drive means for effecting minute adjustments of each end of each arm.

ALBERT T. HARRIS. 

